This invention relates to unsaturated ketones which polymerise on exposure to actinic radiation, to methods of polymerising such ketones by means of actinic radiation and of coating a surface with such ketones, to supports bearing thereon such a ketone in the polymerisable state, and to supports bearing thereon such a ketone polymerised by means of actinic radiation.
Substances capable of becoming polymerised on exposure to actinic radiation are used in, for example, the preparation of printing plates for offset printing and of printed circuits, and for coating metals, such as in the manufacture of cans (see, e.g., Kosar, "Light-sensitive systems: Chemistry and Applications of non-silver halide Photographic processes," Wiley, New York, 1965; Delzenne, "Synthesis and Photocrosslinking of Light-sensitive Polymers" in European Polym. J. Suppl. 1969, pp. 55-91; Williams, "Photopolymerisation and Photo-crosslinking of Polymers" in Forschr. Chem. Forsch. Vol. 13 (2), 227-250). There are various drawbacks in the substances presently available which may be polymerised by exposure to actinic radiation. Some are so unstable that they must be applied to a substrate only immediately prior to exposing them to actinic radiation. Others are relatively insensitive and need lengthy exposure to actinic radiation in order to become sufficiently polymerised. Others, after being polymerised, are not resistant to etching baths used in subsequent processes.
Most previously known substances which polymerise on exposure to actinic radiation are used with a sensitiser such as Michler's ketone (bis(p-dimethylamino)benzophenone), benzoin, or an alkyl ether of benzoin, to shorten the exposure time required for polymerisation. However, the sensitiser alters the electrical properties of the polymer, and may volatilise on being heated under pressure, so making it unsuitable for use in multilayer laminates; in the preparation of these, therefore, the polymer is removed, usually by wire brushing, after the metal etching process has taken place, which removal adds to the cost of the laminates and may cause damage to the surface of the metal.